The present invention relates to an interference detection apparatus and, more particularly, to an interference detection apparatus for use in a digital mobile communications system.
To detect co-channel interference, a conventional apparatus uses a beat phenomenon caused by an interference wave. A reference is made to a paper entitled "A new method of co-channel D/U measurement using squared-law envelope differential detection", vol. 83, No. 3, IEICE Technical Report, by Kozono et al 1983. By detecting and processing a received signal envelope, the apparatus obtains the average power of the received signal and power of the beat component. Based on the obtained powers, the apparatus calculates a desired signal level-to-undesired signal level (D/U) ratio. If the D/U ratio falls below a predetermined level, the apparatus determines that interference exists.
Quality of such an interference detection depends on the linearity of the envelope detector. Thus, if manufacturing errors in the envelope detector occur, they deteriorate the interference detection quality. In addition, the conventional apparatus needs a relatively long time to detect interference, because obtaining the D/U ratio involves a complicated calculation. This detection delay adversely affects communications.